The present invention relates to a process for the treatment of waste water or other aqueous streams contaminated with nitro phenols, and it particularly relates to the chemical treatment of such aqueous streams to degrade dinitrated phenolic contaminants of the formula: ##STR1## (wherein R.sub.1, R.sub.3, and R.sub.5 are nitro, hydrogen, or alkyl groups, R.sub.2 and R.sub.4 are hydrogen or nitro groups, and at least two of said R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5 are nitro groups) into colorless and relatively harmless nonaromatic fragments.
Nitro phenols and the derivatives thereof are commonly encountered contaminants in aqueous waste from various chemical processes. Such compounds have most recently been suggested for use as polymerization inhibitors in petrochemical conversion processes for the production of vinyl aromatic compounds. During the course of such chemical processes, effluent streams contaminated with nitro phenols are frequently produced. Before waste streams contaminated with these compounds can be discharged freely into the environment, however, current pollution control regulations require that the nitro phenolic contaminants be substantially removed therefrom. However, since these substances cannot be broken down by biological means and heretofore have been resistant to simple chemical decomposition, the nitrated phenols have presented a very difficult waste disposal problem.
One approach to this problem is suggested in U.S. Pat. No. 3,617,581, which describes a process for decomposing oxy aromatic contaminants by dissolving excess alkali in the contaminated water, and then contacting the resultant alkaline solution with sufficient chlorine to reduce the pH below 7. Mono nitrated phenols, such as chloronitrophenol are taught as being successfully degraded by this process and, this process is also suggested as suitable for the degradation of dinitro-o-sec-butylphenol. The use of chlorine gas as a degradation agent is undesirable, since in aqueous solution, chlorine forms hypochlorous acid which has a very sharp odor at concentrations of as low as 3.5 parts per million, and is also extremely corrosive.
It is also known in the art that chlorine dioxide may be used for the degradation of phenol. See, for example, U.S. Pat. No. 4,013,761. Similarly, it is described in Chemical Abstracts, Volume 60, No. 14422G and H, that phenol or chlorophenol may be oxidized with 14-18% chlorine dioxide in air to the corresponding quinones in 12-82% yields. It is also described that paranitrophenol may be oxidized with chlorine dioxide in a very small yield. However, this reference teaches that the dinitro- and trinitro phenols are stable to chlorine dioxide treatment, and cannot be decomposed thereby, corroborating the opinion of those skilled in the art that the dinitro- and trinitro phenols are particularly resistant to chemical decomposition and cannot be decomposed by simple chemical treatment.
Accordingly, in view of the large commercial importance of the nitrated phenols, particularly the higher nitrated phenols, and the difficult waste disposal problems associated therewith, there exists a great need in the art for a simple and economical process for treating aqueous streams to remove these contaminants therefrom.